Reflexibility of Light. 167 



points upon the optic nerve, which lies at the 

 back of the eye ; and these points of convergent 

 rays on the optic nerve, are correspondent to the 

 points of the objects from which the rays diverged. 

 Now the pencils of rays strike the mirror, while 

 they are in their divergent state ; and as the 

 angle of reflection is equal to the angle of in- 

 cidence, they are reflected' back in the same state, 

 and converge exactly as they would have done 

 had they not been intercepted by the mirror. 

 As, therefore, we always see objects in the line in 

 which the rays approached us last, the two lines, 

 viz. that which goes from the object towards the 

 mirror, and the reflected line, are united in the 

 mind of the spectator, and the object is con- 

 sequently seen at s, at an equal distance behind 

 the mirror, as the object was before it. To make 

 this clear, however, I shall present you with 

 another diagram. The lines D c, (fig. 55.) are 

 the lines of incidence, c B are the lines of re- 

 flection, and these form equal angles on the 

 surface of the polished mirror; so that all the 

 ray scorning from the object, and falling upon the 

 mirror at c, will strike the eye at B, and the 

 reflected image will thus become visible. Now 

 no object can be seen that does not lie in a 

 straight line from ttfe eye, or, at least, appear to 

 do so. The body D, therefore, when it comes 

 reflected to the eye, will appear to lie in the 

 straight line AA, which, since the angle of in- 

 cidence is equal to that of reflection, will be 



